Nico’s Nuggets: How to Compare Cannabis Grow Lights

Dear High Times,
Most reference books and articles concerning lighting conditions for growing cannabis refer to wattage used in different light sources. Wouldn’t it be better to establish the lumens required or lux necessary for optimal growth? Then one would only have to worry about the spectral outputs of various light sources. I know that lumens units only govern the visible spectrum, and “chlorophyll a” does adsorb into the near ultraviolet. However, do you think it would be better to talk about lumens or lux rather than wattage, since wattage of a light source is dependent upon the electrical efficiency of the source?
— Sincerely, Novizoid via Grow@hightimes.com

Greeting, Novizoid. Thanks for reading HT and writing in with a grow question.

To start, you are correct about the reasoning for discussing wattage of grow lamps, as energy (electricity) consumption is a primary concern for many growers. Whether it is a clandestine, underground grow operation or a larger, commercial format, growers need to know where their power consumption lies for both security and economic reasons. Thus, most high-intensity discharge (HID) grow lamps are manufactured in three primary wattages: 400-, 600- and 1,000-watt bulbs. Of course, today there exists many more options than just these three wattages, but these represent the most commonly used bulbs.

Ample lighting is key to happy gardens, but don’t over do it.

As far as your thoughts on lumens go, many manufacturers also list lumen output as a marketing ploy on their packaging. And while it is a good reference point for comparison relative to other lamps, lumens are actually not an ideal measurement for horticultural purposes. In fact, lumens should be removed altogether from grow lamp consideration. A lumen, while a measurement of a lamp’s intensity, is really a metric used for the human eye. Lumens would be relevant for theater stage or ambiance lighting, but not for plant growth and development.

Metrics used to measure light quality and quantity are often misleading.

Instead, the true measure of light intensity and quality for botany is a term called PAR, or photosynthetically active radiation. This measurement determines how much of a lamp’s light can actually be used by a plant for food (glucose) production in photosynthesis. PAR takes into account both light quality (spectrum) and light quantity (strength or photon energy). Photosynthetic photon flux density, or PPFD, is a similar (and even better) unit of light measurement that plant biologists often use to quantify PAR, using the number of photons (between 400-700 nm) actually received by a leaf’s surface for a specified amount of time.

Measurements from a spectroradiometer show readings in PAR and PPFD.

These are excellent questions you have asked, and every grower should educate themselves on this information before going into a grow shop to buy a light set-up, especially considering that grow lamps are not cheap. Often times, product packaging is contrived for marketing purposes and fashioned for the novice grower in layman’s terms. However, this does an injustice to those of us who want to learn and provide the optimal conditions for plants in order to achieve the maximum potential our favorite strains hold. Understanding light science is one of the most important factors in creating a successful garden!

Want more information on garden lighting? Click HERE for more good reads.

Thanks for reading everyone and remember: Grow… And help the world grow, too!

Got questions? Email ‘em over to Nico at NicosNuggets@hightimes.com and be sure to put “Nico’s Nuggets” in the subject line! (Tip: Before sending a question, try the new Search feature on the HIGH TIMES website. Simply click the “magnifier” icon at the top right and type “Nico + your subject topic” to see if your question has already been answered!)